Showing papers on "Earthquake resistant structures published in 2001"
TL;DR: In this article, an analytical model based on fiber elements was developed for these connections, which was used for inelastic static analyses of interior connection subassembages and dynamic time history analyses of a six-story steel MRF.
Abstract: Steel moment-resisting frames (MRFs) with posttensioned connections are constructed by posttensioning beams to columns using high strength strands. Top and seat angles are added to provide energy dissipation and redundancy under seismic loading. This new type of connection has several advantages, including the following: (1) field welding is not required; (2) the connection stiffness is similar to that of a welded connection; (3) the connection is self-centering; and (4) significant damage to the MRF is confined to the angles of the connection. An analytical model based on fiber elements was developed for these connections. Experimental test results were used to calibrate the model. The model was used for inelastic static analyses of interior connection subassembages as well as dynamic time history analyses of a six-story steel MRF. A self-centering capability and adequate stiffness, strength, and ductility were observed in the results of these analyses. Time history analysis results show that the seismic...
475 citations
TL;DR: In this article, three new configurations that utilize toggle-brace mechanisms to substantially magnify the effect of damping devices so that they can be utilized effectively in applications of small structural drift are presented.
Abstract: Energy dissipation systems are being increasingly employed in the United States to provide enhanced seismic protection for new and retrofit building and bridge construction. The hardware utilized includes yielding steel devices, friction devices, viscoelastic solid devices, and mostly, so far, fluid viscous devices. This hardware has been used in either diagonal or chevron brace configurations. This paper presents three new configurations that utilize toggle-brace mechanisms to substantially magnify the effect of damping devices so that they can be utilized effectively in applications of small structural drift. Shake table testing of a large scale steel model structure and analysis are used to demonstrate the utility of these configurations. The experimental results demonstrate substantial increases in the damping ratio despite the use of small size damping devices, and, accordingly, significant attenuation of the seismic response of the tested stiff structure is observed. Moreover, the experimental resul...
199 citations
TL;DR: In this article, the effects of a tuned mass damper on the modal responses of a six-story building structure were studied and several optimal location indices were defined based on intuitive reasoning, and a sequential procedure was proposed for practical design and placement of the dampers in seismically excited building structures.
Abstract: Effects of a tuned mass damper on the modal responses of a six-story building structure are studied first to demonstrate the damper's ineffectiveness in seismic applications. Multistage and multimode tuned mass dampers are then introduced. Several optimal location indices are defined based on intuitive reasoning, and a sequential procedure is proposed for practical design and placement of the dampers in seismically excited building structures. The proposed procedure is applied to place the dampers on the floors of the six-story building for maximum reduction of the accelerations under a stochastic seismic load and 13 earthquake records. Numerical results show that the multiple dampers can effectively reduce the acceleration of the uncontrolled structure by 10–25% more than a single damper. Time-history analyses indicate that the multiple dampers weighing 3% of total structural weight can reduce the floor acceleration up to 40%. The multiple dampers can even suppress the peak of acceleration responses due ...
162 citations
TL;DR: In this article, the performance of several modular-block reinforced soil retaining walls and reinforced slopes at the vicinity of the fault was evaluated and the failure cases were highlighted and the cause of failure was identified.
125 citations
TL;DR: In this paper, the authors evaluated the seismic performance of the base-isolated fire command and control (FCC) building during the 1994 Northridge earthquake and the effect of impact.
Abstract: The base-isolated Fire Command and Control (FCC) building in Los Angeles experienced strong motion during the 1994 Northridge earthquake. The California Strong Motion Instrumentation Program has instrumented the building and recorded the data during the Northridge earthquake; these data are available for performance evaluation. Impact was observed in the base-isolated FCC building during the Northridge earthquake. The objective of this study is to evaluate the seismic performance of the base-isolated FCC building during the 1994 Northridge earthquake and the effect of impact. New analytical modeling techniques are developed to analyze the base-isolated FCC building with impact and are verified using system identification. The response computed, using the developed analytical modeling techniques, is verified using recorded data. The response with and without impact is presented. The effects of impact on the structural response are evaluated. The seismic performance evaluations, comparing the response of th...
113 citations
TL;DR: In this article, the authors developed a new seismic damage index based on cumulative member ductility that employs the concept of primary and follower load cycles to distinguish loading history effects, and incorporated the damage index in a methodology that combines nonlinear time history and gravity load stability analyses to evaluate collapse prevention performance as a function of earthquake ground motion intensity.
Abstract: Damage and stability assessment techniques are developed for evaluating the seismic performance of composite steel-concrete moment frames. The approach features a new seismic damage index based on cumulative member ductility that employs the concept of primary and follower load cycles to distinguish loading history effects. Equations are presented to determine the limiting rotation capacity for RC columns, steel and composite beams, and composite steel-concrete connection subassemblages, and the resulting damage model is validated by comparisons with published test data. The damage index is incorporated in a methodology that combines nonlinear time history and gravity load stability analyses to evaluate collapse prevention performance as a function of earthquake ground motion intensity. In contrast to existing seismic assessment procedures, the proposed methodology integrates the destabilizing effects of local damage indices to evaluate overall system response. The assessment technique is illustrated through a trial design study of a six-story frame conducted under Phase 5 of the U.S.-Japan Cooperative Research Program on composite and hybrid structures.
86 citations
60 citations
TL;DR: In this article, the authors discuss the impact of recent amendments in the ACI 318-99 that affect the estimation of nominal beam flexural capacity in seismic design of frame connections.
Abstract: Recent amendments in the ACI 318-99 that affect the estimation of nominal beam flexural capacity in seismic design of frame connections were the motivation for this paper These changes concern the width of slabs considered effective in beam flexure and represent the culmination of a 15-year concerted research effort aimed at understanding and quantifying slab participation in the lateral load resistance of frames through observed experimental findings By accounting for slab participation, the Code recognizes the diaphragm action of slabs in the seismic response of frames, particularly when the slab is on the tension face of the beam Until recently, it was an established design practice to neglect the presence of the slab in estimating beam stiffness and strength, except when the slab was located in the compression zone of the beam Experimental evidence showed that this practice resulted in gross underestimation of beam flexural strength in the assumed plastic hinge regions This paper reviews the practical implications of the recent amendments in the sequence of seismic design and in assessment of the resulting response of reinforced concrete frame structures The effects (of supply and demand) on strength and deformation capacity of the various mechanisms of response, and the hierarchy of failure modes in slab-beam-column connections are discussed
47 citations
TL;DR: In this paper, a finite-element analysis of a model segmental wall subjected to earthquakelike loading generated by a shake table was performed using the computer program DYNA3D, using a simple model to simulate the nonlinear hysteretic behavior of soil, are consistent with observed results from laboratory shake table tests on segmental walls.
Abstract: Block-faced geosynthetic reinforced soil retaining walls, referred to as “segmental” retaining walls, have been extensively used in recent years as permanent civil engineering structures. The disjointed concrete facing blocks are held together through interface friction and concrete keys or mechanical connectors. Because of the disjointed nature of the facing blocks, the design of the segmental wall must consider the available shear resistance between these blocks. Connection capacity must also be considered. Of concern also is the permanent deformation of the segmental wall face following an earthquake. This paper describes a finite-element analysis of a model segmental wall subjected to earthquakelike loading generated by a shake table. The finite-element analysis used the computer program DYNA3D. Results from DYNA3D, using a simple model—Ramberg-Osgood model—to simulate the nonlinear hysteretic behavior of soil, are consistent with observed results from laboratory shake table tests on segmental walls.
41 citations
36 citations
Book•
01 Jan 2001
TL;DR: In this article, the authors present the latest ideas and findings on the inelastic behavior of reinforced concrete (RC) structures from the analysis and design standpoints, as well as design issues that can improve the seismic performance of these structures.
Abstract: Proceedings of the U.S.–Japan Seminar on Post-Peak Behavior of Reinforced Concrete Structures Subjected to Seismic Loads: Recent Advances and Challenges on Analysis and Design, held in Tokyo and Lake Yamanaka, Japan, October 25-29, 1999. Sponsored by the National Science Foundation, U.S.A.; Japan Society for the Promotion of Science; Japan Concrete Institute. This collection presents the latest ideas and findings on the inelastic behavior of reinforced concrete (RC) structures from the analysis and design standpoints. These papers discuss state-of-the-art concrete material models and analysis methods that can be used to simulate and understand the inelastic behavior of RC structures, as well as design issues that can improve the seismic performance of these structures. Topics include modeling of concrete behavior; modeling of RC structures (finite element approach and macro-element approach); and experimental studies, analysis, and design issues.
TL;DR: In this article, the authors derived the amount of transverse reinforcement necessary so that hoop fracture and fatigue fracture of the longitudinal bars coincide for critical earthquake motions, using an energy-based approach coupled with notions of low-cycle fatigue.
Abstract: Potential plastic hinge zones in confined concrete columns require that sufficient transverse reinforcement be provided to avert undesirable failure modes and to ensure dependable inelastic (ductile) behavior in earthquakes. Conventional code–based approaches for detailing confining reinforcement are founded on the premise of preserving axial load before and after spalling of the cover concrete. Such formulations account for neither the cyclic actions nor the duration effects of ground motions. This paper derives the amount of transverse reinforcement necessary so that hoop fracture and fatigue fracture of the longitudinal bars coincide for critical earthquake motions. An energy–based approach coupled with notions of low–cycle fatigue are used for this purpose.
TL;DR: In this article, a three-dimensional finite element analysis of the seismic behavior of micropiles used in engineering applications, such as construction in earthquake areas, and seismic retrofitting of structure foundation and retaining systems, is presented.
Abstract: Presented is a three-dimensional finite element analysis of the seismic behavior of micropiles used in engineering applications, such as construction in earthquake areas, and seismic retrofitting of structure foundation and retaining systems. It is composed of two parts. The first is concerned with analysis of the seismic behavior of a single micropile supporting a superstructure; results obtained with three-dimensional finite element modeling are compared to those obtained from a simplified model based on the Winkler approach. The second part includes a study of the seismic behavior of groups of micropiles. Numerical simulations are conducted to study the variation of the group effect with the variation of micropile spacing, number of micropiles, and the position of the micropile in the group. Analysis of results of numerical simulations shows that the presence of the superstructure induces significant inertial effect, which causes a high increase in the bending moment in the upper part of micropiles; th...
01 Jan 2001
TL;DR: In this paper, the authors introduced the analytical calculation and experimental test results of shear failure circular section reinforced concrete (RC) bridge columns retrofitted by CFRP jacketing for the failure.
Abstract: The merits of CFRP (carbon fiber reinforced polymer) include anti corrosion, lightweight, easy cutting and construction as well as high strength and high elastic modulus. This paper introduces the analytical calculation and experimental test results of shear failure circular section reinforced concrete (RC) bridge columns retrofitted by CFRP jacketing. The constitutive model introduced in this paper was based on the Mohr-Columb failure envelope of the soil under tri-axial test with lateral confinement. Introduced are the seismic retrofit design analytical calculation and the experimental tests of the bridge column retrofitted by CFRP jacketing for the failure. The results show a substantial improvement in the seismic performance from the retrofit as well as a change in the failure mode of the bridge columns.
01 Jan 2001
TL;DR: In this article, a technique based on fiber reinforced polymer (FRP) laminate and bar external installation for the seismic upgrade of reinforced concrete beam-column joints is presented, which is tested with an experimental program on 11 under-designed interior connections, obtaining selective upgrade while choosing different combinations and locations of sheets and bars in order to obtain different structural performance of joints.
Abstract: The upgrade of seismic performance of existing reinforced concrete (RC), gravity load designed (GLD) structures is an important issue that involves economic as well as social aspects in different areas of the world. The strength hierarchy governs the upgrade requiring to protect the column and the panel so that the formation of a plastic hinge during a seismic event is in the beam. Presented is a technique based on FRP (fiber reinforced polymer) laminate and bar external installation for the seismic upgrade of RC beam-column joints. The technique was tested with an experimental program on 11 under-designed interior connections, obtaining selective upgrade while choosing different combinations and locations of sheets and bars in order to obtain different structural performance of joints. The paper summarizes selected results to underline how different parameters influenced the behavior of the joint in terms of strength and/or ductility.
TL;DR: In this article, the performance-based earthquake engineering of structural wall buildings is examined from the per- spective of achieving performance-oriented earthquake engineering. But, although strain limits are present in the 1997 UBC, the drift ratio limits generally govern design, and the conflict between assumed force reduction factors and actual ductility demand at the design limit state controlled by drift is explored.
Abstract: The seismic provisions of the 1997 Uniform Building Code (UBC) are examined from the per- spective of achieving performance-based earthquake engineering of structural wall buildings. It is shown that although strain limits are present in the 1997 UBC, the drift ratio limits generally govern design. The conflict between assumed force reduction factors and actual ductility demand at the design limit state controlled by drift is also explored. Through the use of design examples and dynamic inelastic time history analysis it is shown that attempts to achieve performance-based engineering with a force-based approach such as that described in the 1997 UBC will inevitably not be possible. As an alternative, it is shown that a simple and more rational direct displacement-based approach would better achieve the objectives of performance-based earthquake en- gineering.
TL;DR: In this paper, a large-scale concrete multiple-column bridge bents were designed and subjected to simulated earthquake loading at the University of California-San Diego (UCSD).
Abstract: In the aftermath of widespread bridge damage in recent California earthquakes, a significant amount of research has been conducted to improve seismic performance of bridge structures. Compiling recent advances, 2 large-scale concrete multiple-column bridge bents were designed and subjected to simulated earthquake loading at the University of California-San Diego. In addition to serving as proof-test specimens, the bridge bents facilitated examination of improved cap beam-to-column joint reinforcement details to minimize construction problems. The design of the joints in the 1st test unit was simplified by using prestressing in the bent cap and examining the force transfer across the joint, which also enabled introduction of precast construction for concrete multiple column bents. In the 2nd test unit, joint reinforcement was minimized by utilizing efficient joint force transfer models and special reinforcement products. Design details, seismic performance, and selected test results are discussed.
TL;DR: In this paper, a simple and efficient method is presented for proportioning of regular, moderate-rise reinforced concrete building structures, where member sizes are selected based on the demand defined by the displacement spectrum and criteria specified in relation to drift response.
Abstract: A simple and efficient method is presented for proportioning of regular, moderate-rise reinforced concrete building structures. The method differs from conventional procedures in that member sizes are selected based on the demand defined by the displacement spectrum and criteria specified in relation to drift response. The maximum mean drift, or average distortion over the total height, is limited to reduce the expected damage to the structure. A series of analytical reinforced concrete frames are proportioned and tested using a suite of ground motions. Results of the analyses indicated that maximum displacement responses of the proportional frames were within the specified drift limit when a maximum-allowable period criterion was satisfied.
TL;DR: In this article, a simplified analysis procedure has been developed to consider accidental torsion in building design that is rational and convenient relative to building codes, which is extended and evaluated in this paper against measured accidental Torsion determined from motions of 12 buildings with nominally-symmetric plan.
Abstract: A simplified analysis procedure has been developed to consider accidental torsion in building design that is rational and convenient relative to building codes. This procedure is extended and evaluated in this paper against measured accidental torsion determined from motions of 12 buildings—with nominally-symmetric plan—recorded during Northridge (1994), Loma Prieta (1989), Whittier (1987), and Upland (1990) earthquakes. The selected buildings include structures in reinforced concrete and in steel that cover a wide range of structural systems, including moment resisting frames, shear walls, braced frames, and hybrid systems. After the measured torsion is interpreted and compared to analytical estimates, it is demonstrated that this procedure is sufficiently accurate to be used in design applications.
TL;DR: In this paper, a review of the development in the area of controlled civil structures and highlights a robust control perspective in active vibration suppression control of flexible structures, considering a grey box approach in the system identification process.
Abstract: The main trend in structural technology is to change from conventional earthquake resistant structures, which are designed 'not to collapse even under the strongest earthquake' to structural controlled buildings, which are designed 'to suppress the vibrations itself'. Indications are that control methods will be able to make a genuine contribution to this problem area, which is of great economic and social importance. Current researches in the field of active structural control focus on: system identification, model order reduction, limited control authority, available measurements etc. The article reviews some of the developments in the area of controlled civil structures and highlights a robust control perspective in active vibration suppression control of flexible structures, considering a grey box approach in the system identification process.
14 Mar 2001
TL;DR: In this paper, the authors studied the behavior under seismic loading of multiple-anchor connections to concrete and found that the connections designed for ductile behavior in uncracked concrete under static loading will probably still behave in a ductile manner in cracked concrete under dynamic loading.
Abstract: The aim of the research program discussed here was to study the behavior under seismic loading of multiple-anchor connections to concrete. The static and dynamic behavior, under tension and shear (separately and combined) of single and multiple-anchor connections to concrete are discussed. Effects of cracking and dynamic loading rates were addressed. The paper also deals with the seismic response of multiple-anchor connections to concrete. Its most important conclusion is that multiple-anchor connections designed for ductile behavior in uncracked concrete under static loading will probably still behave in a ductile manner in cracked concrete under dynamic loading.
TL;DR: In this paper, an evaluation of the seismic performance and retrofit of reinforced-concrete bridge columns with structural flares is presented. But the results indicate that some of the existing methods for evaluating the shear capacity of columns can be unconservative and could overestimate the capacity of the columns included in this study by 60%.
Abstract: This paper presents an evaluation of the seismic performance and retrofit of reinforced-concrete bridge columns with structural flares. Experimental and analytical studies were performed on four 40%-scale specimens. Two specimens represented the as-built columns, while the other two were retrofitted with steel jackets for shear capacity enhancement. The results indicate that some of the existing methods for evaluating the shear capacity of columns can be unconservative and could overestimate the shear capacity of the columns included in this study by 60%. It is also shown that by implementing proper detailing, steel jackets can be used to enhance the shear capacity and ductility of flared columns with no appreciable increase in the shear demand.
TL;DR: In this paper, a simple method is proposed to enhance the ductility of beam-to-column connections of existing buildings by trimming the bottom flange of the beam slightly.
Abstract: The fracture of beam-to-column connections of steel buildings in the Northridge and Kobe earthquakes generated concerns about the reliability of current design and construction technology for steel connections. The same type of fracturing may occur at similar beam-to-column connections of steel buildings in other seismically active areas. A simple method is proposed here to enhance the ductility of beam-to-column connections of existing buildings. By trimming the bottom flange of the beam slightly, the ductility of the connection can be greatly improved. Experimental studies of the newly designed connections under cyclic load show that the ultimate strengths are almost unaltered; however, the plastic rotational capacity can be increased significantly. When adopting the proposed method, the only work needed is to trim part of the bottom flange plate, and this can be done without removing the floor slab. The proposed connection method can be easily implemented to enhance the ductility of beam-to-column conn...
TL;DR: In this article, first hand observations of reconnaissance team that visited the site in February 2001 were used to assess the performance of precast concrete construction and the building code situation in India.
Abstract: The devastating earthquake that struck the Kutch area in Gujarat, India on January 26, 2001, was the most severe natural disaster to afflict India since her independence in 1947. The devastation was major in terms of lives lost, injuries suffered, people rendered homeless, as well as economic impacts. This report is based on first hand observations of reconnaissance team that visited the site in February 2001. Additional information was gathered from several sources, including other visiting teams, news reports and technical literature. The paper touches upon seismological/geotechnical aspects of the earthquake and discusses the performance of engineered buildings. Precast concrete construction, including non-building uses of precast concrete, is discussed. In concluding the paper, the building code situation in India is briefly commented upon.
TL;DR: The south connector bridge in the I-5/State Route 14 interchange failed during the 1994 Northridge (California) earthquake because of concentration of shear forces in the short columns near the abutments as discussed by the authors.
Abstract: The south connector bridge in the I-5/State Route 14 interchange failed during the 1994 Northridge (California) earthquake because of concentration of shear forces in the short columns near the abutments. In the replacement bridge, the column heights were made uniform and other changes were made with respect to supports near the expansion hinges and hinge connectivity. In this study, the nonlinear seismic response history of a bridge model based on the new bridge was evaluated relative to that of a conventional bridge. Additional studies were conducted to determine if the conclusions presented here are also valid for skewed bridges. Results show that the new design is successful in accomplishing a uniform shear distribution in columns only if abutment shear keys are designed to fail under moderate amplitude ground motions. The lack of continuity in the hinge is a drawback of the new design as it led to large differential displacements at the hinge.
TL;DR: In this paper, the authors proposed a curved cable-stayed bridge with a single canted tower, which consists of a multicell steel box girder with composite concrete-steel deck.
Abstract: The innovative bridge design discussed in this paper is a long-span curved cable-stayed bridge with a single canted tower. The superstructure of the bridge consists of a multicell steel box girder with composite concrete-steel deck. The single tower of the bridge is a multicell steel box with the core cell dedicated to the service elevator and stairs. The outer cells of the single tower are filled with high-strength concrete to provide strength and stiffness in a composite action. The foundation of the main single tower is a solid footing embedded in the rock. Inelastic time-history analyses were conducted to complete the seismic design and establish expected seismic performance. After a description of the architectural design, seismological, geotechnical, and structural design aspects are discussed, and a summary of seismic design and expected seismic response of the curved cable-stayed bridge concept is presented.
18 May 2001
TL;DR: In this paper, an extensive research program underway at the University of Toronto, effectiveness of fiber reinforced polymers in enhancing structural performance both in terms of strength and ductility is investigated.
Abstract: Retrofitting of concrete structures with fiber reinforced polymers is a relatively new technique. In an extensive research program underway at the University of Toronto, effectiveness of FRP in enhancing structural performance both in terms of strength and ductility is being investigated. The structural components tested include columns, beams, slabs and bridge culverts. Research on columns has focussed on improving their seismic resistance by confining with FRP. Results from a select group of eight circular and four square columns are presented here. All the columns were subjected to simulated seismic loads. Based on a comparison of the moment-curvature responses of the critical sections of FRP-retrofitted specimens with those of similar companion specimens with FRP, it can be concluded that FRP wraps significantly improved the seismic resistance of columns.
Journal Article•
TL;DR: In this article, an experimental and analytical investigation was conducted to evaluate the effectiveness of isolating the superstructure from the substructure of a highly skewed prestressed concrete (P/C) slab on a girder bridge.
Abstract: Experimental and analytical investigations were conducted to evaluate the effectiveness of isolating the superstructure from the substructure of a highly skewed prestressed concrete (P/C) slab on a girder bridge. Dynamic testing of the bridge was performed using the pullback, quick-release method. A 3D finite elemental model of the bridge was calibrated and refined to match experimentally determined natural frequencies and mode shapes. Time-history analyses, using site-specific acceleration records, were conducted for the seismically isolated bridge model and an identical nonisolated bridge model. Seismic isolation was found to appreciably reduce forces that the bridge substructure and foundation must resist. When compared to the nonisolated bridge for the design earthquake (or 50-year event), the maximum pier moments were reduced between 32% and 62%, and the maximum shears were reduced between 30% and 66%.